Description of the Prior Art
Apparatus for mixing pulp and fluid, e.g. oxygen or ozone, is known through SE 436 652, SE 459 904, SE 462 857, U.S. Pat. No. 3,095,349 and U.S. Pat. No. 4,886,577, for instance. In the known apparatus one of the gap-forming wall elements is arranged to rotate and therefore requires a driving motor and foundation for its installation. These apparatus therefore require relatively much place and the installation is relatively time-consuming. Furthermore, it is impossible to automatically alter the through-flow area of the gap during operation in order to set optimal mixing conditions and capacity or to remove any clogged fibre material without dismantling the apparatus.
When bleaching pulp with ozone, for instance, relatively large amounts of gas containing ozone must be added since the carrier gas can only contain limited quantities of ozone. Furthermore, it must be taken into account that ozone reacts extremely quickly with the pulp and must therefore be mixed with it so that if possible all parts of the pulp are treated with ozone. In the known apparatus as described in the above-mentioned patent specification relating to mixing in ozone, the ozone is supplied to the pulp at one or more points as it flows past the supply points so that certain parts of the pulp are mixed with ozone while other parts are not treated with any ozone, or only with a limited quantity due to insufficient mixing effect in the apparatus and/or because all or almost all the ozone has been consumed when the carrier gas reaches these other parts of the pulp as well.